The Design Of Mesoporous Molecular Sieves SBA-15 Supported Bimetal And Application For Photocatalytic Epoxidation Of Styrene

Use of mesoporous molecular sieves has attracted considerable attention due to their unique properties, especially catalysis involving large molecules. Acid-base properties and redox functions could be generated by the incorporation of heteroelements as extra-framework nanoscale oxide clusters or in their appropriate valence state. It was also vital to introduce transition metal elements in the mesostructure materials. The incorporation of two different metals might therefore create new functional materials with different or new redox and acid properties. However, only few publications have proposed the synthesis of bimetallic ions modified mesoporous molecular sieves based on synergistic effect of metal ions. Therefore, this dissertation aimed at developing highly dispersed bimetal composite mesoporous materials with high efficiency, followed by application for photocatalytic epoxidation of styrene employing H₂O₂ as oxidant under low temperature. By means of versatile characterization techniques, physical and chemical structures of catalyst were investigated at length. Also, the relationship between catalytic performance and microstructure of catalyst was explored.The major work and achievement in this dissertation were as follows:1. Preparation and application of V-SBA-15 modified by alkaline-earth metalsV-SBA-15 mesoporous molecular sieves modified by alkaline-earth metals were successfully prepared by means of incipient wetness method, and the resulting were characterized by XRD, N₂-isothermal absorption and desorption, SEM, TEM, ²⁹Si CP-MAS NMR, XPS, NH₃-TPD, H₂-TPR and so on. The characterization results indicated that active centres were highly dispersed on mesoporous molecular sieves. At the same time, Alkaline-earth metal ions enhanced the selectivity of styrene oxide for photocatalytic epoxidation of styrene by two ways: the addition of alkaline-earth metal ions to V/SBA-15 dispersed polymeric species and suppressed deep oxidation of styrene oxide; alkaline-earth metals decreased the acidic sites of V/SBA-15 to avoid ring-opening. Moreover, with the increase of metallic characteristics from Mg to Ba, the photocatalytic result of catalysts presented good regularity. The influence of reaction parameters, such as the molar ratio of H₂O₂/styrene, reaction time, the amount of catalyst, metallic oxide loading, on the conversion of styrene and selectivity of styrene oxide have also been studied in details. The results revealed that Mg-V/SBA-15 was more active than other catalysts.2. Preparation and application of Cu-Zn/SBA-15First of all, mesoporous SBA-15 were synthesized by template method. The next thing was the preparation of Cu-Zn/SBA-15 using impregnation method. Catalysts were characterized by low-angle XRD, N₂-isothermal adsorption desorption, SEM, TEM, ²⁹Si CP-MAS NMR and XPS and so on. The characterization results indicated that active metals were highly dispersed on the mesoporous SBA-15. However, there was barely photocatalytic activity of epoxidation of styrene about the catalysts of Cu-Zn/SBA-15. In the reaction system, the addition of trace H+ dramaticlly enhanced the selectivity of styrene oxide and the conversion of styrene for photocatalytic epoxidation of styrene. Even the selectivity of styrene oxide reached more than 80%.